Ally McCoist reckons "arrogant" Celtic treated 10 In A Row like a mere formality.
The Parkhead club have parted company with boss Neil Lennon after his side slipped 18 points behind Rangers in the Premiership title race.
The Irishman resigned following Sunday's defeat to Ross County as the club's decade of dominance dream surely slipped out of reach.
Ibrox legend McCoist insists he wouldn't include Lennon in his accusations of overconfidence but believes he must still take his share of responsibility for a disastrous campaign.
He told talkSPORT: "The first thing I've got to say is I hope he can get a bit of sanity back in his life, go enjoy himself and relax with his family for a period.
"That's the one thing, looking at Neil, I think he needs and probably wants. That's the most important thing, to spend a bit of quality time, relax and get away from the insane pressure that is being an Old Firm manager.
"In terms of the decision itself, I'm not overly surprised at all.
"The way the season has gone for Celtic has been one disaster after another. There's a lot of people responsible for that.
"Neil, being the manager, will be one of them; the people above him as well and, indeed, the players have got to shoulder a lot of the responsibility.
"It was a massive season for them. You'd have to say, clearly, it looks as though the league has gone and the league was the big one.
"Everybody at Celtic wanted the magical figure of 10 for some time now. It doesn't look as though that's going to be the case.
"I always felt there was - not from Neil - an element of arrogance coming from within Celtic. They thought it was just a formality to win 10 In A Row.
"Clearly, that hasn't been the case and the supporters are very, very angry. Obviously, it's cost Neil his job.
"This news, we had a rough idea on Wednesday night that it was going to break and it's not come as a major surprise at all."
